Figure 4

Model-calculated evolution of pH near WSI and burrow wall during each rest–ventilation cycle of N. diversicolor. At the beginning of each rest period (T1 = 0 min), the pH along burrow wall is 8.0. It decreases during the rest period, as seen at halfway into the rest period (T2 = 2.3 min), and at the end of the rest period (T3 = 4.6 min) when the pH at burrow wall is as low as 6.9. Immediately following the rest period, the macrofauna begins ventilation (T4 = 4.6 Δ min; Δ is equal to one time step in the model run, which is 8 in these simulations) resulting in the maintenance of the burrow water pH level, as seen at halfway into the ventilation period (T5 = 6.9 min) and at the end of each rest–ventilation cycle (T6 = 9.3 min).